1. Field of the Invention
The present invention relates to a process for preparing high purity metals such as Mo, W, Nb, Zr, Cu, Zn, Ni, Co and In.
2. Description of the Prior Art
Conventionally Mo and W have been prepared by reducing their oxide in a hydrogen atmosphere. However, the disadvantage is that a temperature as high as 1000.degree. to 1100.degree. C. is required for the reduction and the purification procedure prior to obtaining their oxides are complicated. Such metals as Ni and Zn are prepared by leaching with an acid, followed by separation and purification by means of the solvent extraction technique, and by then electrolysis. The disadvantage is much consumption of electrical energy. Zn may be prepared by the reductive distillation at a high temperature, but a rather complicated process of distillation is necessary because of difficult separation from other metals. Cu is prepared generally in the form of crude metal by treating sulfide ores directly in a vertical or reflection furnace followed by the electrolytic purification. However, this process cannot be applied to low quality ores nor to oxide minerals of Cu and only limited kinds of ores are employed as raw material.
Further fine powders of these metals could be obtained by crashing their metal in a stream of hydrogen or an inert gas. But not a little mechanical as well as human energy are required to produce a powder of less than 40.mu. diameter, and a superfine powder of less than 1.mu. could not be obtained by any mechanical means.
Superfine powders of Cu, Ni and Co could also be produced by directly reducing with a hydrogen gas their ions in an aqueous solution, but the process requires a high temperature and pressure and an apparatus of a complicated structure. Furthermore it is difficult to prevent the metal powder from re-oxidation.